1. Background Of The Invention
1.1. Technical Field
1.2. Description Of Related Art
2. Summary Of The Invention
3. Description Of The Preferred Embodiments
3.1. Examples 1 to 6
3.2. Example 4
3.3. Example 5
3.4. Example 6
3.5. Examples 7 through 20
3.6. Examples 21 through 24
3.7. Example 25
3.8. Examples 26 through 30
3.9. Examples 31 through 32
4. Claims
5. Abstract Of The Disclosure
1.1. Technical Field
The present invention relates to an initiation system for anionic (co)polymerization of (meth)acrylic, vinylaromatic and/or diene monomers; this new initiation system has proven to be high-performance, because it uses easy experimental conditions as regards temperature, with practically a quantitative yield, and, for example, permits simple synthesis of poly(methylmethacrylate) (PMMA) with a high content of isotactic triads (at least 75%), with a high number average molecular weight ({overscore (Mn)}), while retaining a narrow polymolecularity index Ip ({overscore (Mw)}/{overscore (Mn)}), and also controlled polymerization of acrylates, particularly primary acrylates, and the synthesis of block copolymers with blocks of isotactic PMMA and the synthesis of polydienes with high contents of the 1,4-microstructure.
1.2. Description of Related Art
In the literature, initiation systems permitting anionic polymerization of methacrylates with a high level of isotactic triads all present one limitation. This is in the area of yields, i.e., at the level of the main characteristics of polymers (Ip, {overscore (Mn)}, tacticity). Experimental conditions are generally drastic, notably requiring very low temperatures (xe2x88x9278xc2x0 C.). Thus, in Polymer Journal, Vol. 17, No. 8, pp., 977-980 (1985), and in Polymer Journal, Vol. 18, No. 12, pp. 1037-1047, HATADA et al. report that t-C4H9MgBr prepared in diethyl ether has not caused any secondary reactions in the polymerization of methylmethacrylate in toluene at xe2x88x9278xc2x0 C., and has formed a highly isotactic polymer with a narrow polymolecularity index. However, this process is limited to very low temperatures and does not permit synthesis of PMMA with very high molar masses.
There is, therefore, a real need in this area for more flexible operating constraints and an improvement in the processes or characteristics of the products.
The present invention relates to an initiation system composed of the reaction product of at least one cyclic siloxane and at least one organometallic compound of sufficient reactivity to open the siloxane ring.
Application of the present invention is to the preparation of homopolymers of (meth)acrylic, vinylaromatic or diene monomers, random or block copolymers of these monomers and, in particular, application to poly(methylmethacrylate) with a high content of isotactic triads.
The first objective of this invention therefore is an initiation system for anionic (co)polymerization of (meth)acrylic, vinyl-aromatic and/or diene monomers, including the reaction product
a) of at least one cyclic siloxane of Formula I: 
wherein R and Rxe2x80x2, identical or different, each represent a C1-C8, linear or branched alkyl radical, or an aryl radical, an arylalkyl or alkylaryl radical, wherein the alkyl group has from 1 to 6 atoms of carbon and p is a whole number from 3 to 6 and
b) of at least one organometallic compound with sufficient reactivity to open the siloxane ring,
the molar ratio r=no/n, wherein n0 is the number of moles of active sites deriving from the organometalic compound reacting with n moles of cyclic siloxane compound, being between 0.8p and 2p, where p represents the number of siloxane units.
In Formula (I) for cyclic siloxane, R and Rxe2x80x2, identical or different, preferably represent a methyl radical, and p, representing the number of siloxane units, preferably is equal to 3 or 4. A particularly preferred cyclic siloxane, called Dp, with D=xe2x80x94(R)(Rxe2x80x2)Sixe2x80x94Oxe2x80x94 and p=the number of these units, particularly preferably, is hexamethylcyclotrisiloxane (D3) or octamethylcyclotetrasiloxane (D4).
The organometallic compound is selected, in particular, from among the compounds:
(1) of Formula (II):
(R1)uxe2x80x94Mxe2x80x83xe2x80x83(II) 
wherein:
R1 represents a branched-chain alkyl radical containing 3 to 6 carbon atoms; or an aryl radical with one or more rings, possibly substituted; or an alkenyl radical at C2-C6, substituted by aryl or alkylaryl; or an alkyl radical, linear or branched, containing 1 to 6 carbon atoms, substituted by at least one phenyl group, or a C1-C6 alkylaryl radical, wherein the alkyl group has from 1 to 8 carbon atoms;
M designates an alkaline metal or alkaline earth metal; the valence u is respectively 1 or 2.
(2) difunctional compounds of Formula (III): 
wherein:
Mxe2x80x2 is an alkaline metal;
R2 represents an organic bivalent radical, whether aliphatic, cycloaliphatic, aromatic or containing at least one cycloaliphatic or aromatic group; R2 may contain substituents;
R3 and R4 each independently represent an organic monovalent radical, whether aliphatic, cycloaliphatic, aromatic or containing at least one cycloaliphatic or aromatic group, R3 and R4 may contain substituents;
(3) monofunctional silylated compounds of Formula (IV): 
wherein:
R5, R6, R7 each independently represent an alkyl radical, linear or branched, containing 1 to 6 carbon atoms;
R8 represents an alkylene radical, linear or branched, containing 1 to 6 carbon atoms;
Mxe2x80x3 designates an alkaline metal or alkaline earth metal, and valence q is 1 or 2, respectively; and
(4) difunctional silylated compounds of Formula (V): 
wherein:
R9 and R10 each independently represent a linear or branched alkyl radical containing 1 to 6 carbon atoms;
R11 and R12 each independently represent a linear or branched alkylene radical containing 1 to 6 carbon atoms; and
Mxe2x80x2xe2x80x3 designates an alkaline metal.
The monofunctional initiators (1) of Formula (II) are selected, in particular, from between sec.-butyllithium and tert.-butyllithium.
As for difunctional compounds (2) of Formula (III), they are selected notably from between 1,1,4,4-tetraphenyl-1,4-dilithiobutane and 1,1,4,4-tetraphenyl-1,4-disodiobutane.
In Formulas (IV) and (V) above, it is preferable for R5, R6, R7, R9 and R10 to each represent a methyl, and for R8, R11 and R12 to each represent a methylene, and for Mxe2x80x3 and Mxe2x80x2xe2x80x3 to each represent lithium.
Difunctional precursors, such as lithium naphthalene, sodium naphthalene and potassium naphthalene also are used.
The inventive initiation system is generally obtained by reaction of at least one cyclic siloxane Dp with at least one organometallic compound at ambient temperature, under nitrogen, in a nonpolar solvent such as toluene. The mechanism of this reaction is that of a nucleophilic addition reaction of the organometallic compound to the electrophilic silicon atom, thus provoking the opening of the ring.
As an example, with n moles of cyclic siloxane D3 (3 siloxane units) and n0 moles of active sites deriving from organometalic compound R1M reacting with the cyclic siloxane D3, the reaction is as follows: 
Since the medium is nonpolar, it is thought that there are associated mixed species of the form xR1M and 6-x R1-D-M with D: 
Due to the existence of several associated mixed species, preparation of the initiation system, at ambient temperature, requires enough time to permit an equilibrium favorable to the thermodynamically most stable species to be reached. This period may, for example, be 20 hours.
The choice of the molar ration r=no/n permits control of the molar ratio (R) of the silanolate species (S) obtained related to the organometallic compound acting as initiator (A) and consequently constitutes a parameter that affects this equilibrium.
The quantity of siloxane units p must be sufficient to permit formation of a complex with the active polymerization core and thus allow stabilization of the latter.
The quantity of siloxane units p depends on the organometallic compound chosen and the monomer(s) to be polymerized. The molar ration no/n is thus preferably between 0.8p and 2p.
The following initiation systems is cited advantageously: one prepared from sec.-butyllithium (sec.-BuLi) and hexamethylcyclotrisiloxane (D3), one prepared from tert.-butyllithium (tert.-BuLi) or trimethylsilylmethyllithium (TMSM-Li) and hexamethylcyclotrisiloxane (D3), one prepared from sec.-BuLi and octamethylcyclotetrasiloxane (D4) and one prepared from tert.-BuLi or TMSM-Li and D4.
This invention also concerns an anionic (co)polymerization process for (meth)acrylic, vinylaromatic and/or diene monomers, characterized in that the polymerization is conducted in the presence of an initiation system as defined above.
The polymerization temperature varies between about xe2x88x9278xc2x0 C. and +25xc2x0 C. and is preferably below about xe2x88x9220xc2x0 C. for acrylates and about 0xc2x0 C. for methacrylates.
The polymerization, conducted in the presence of the inventive initiation system, preferably takes place in the absence of moisture and oxygen, and in the presence of at least one aprotic solvent, polar or nonpolar, and preferably mostly nonpolar, preferably selected from among benzene, toluene, ethylbenzene, tetrahydrofuran, diglyme, tetraglyme, orthoterphenyl, biphenyl, decaline, tetraline or mixtures thereof; toluene or ethylbenzene may be used advantageously. A mixture of toluene-tetrahydrofuran or ethylbenzene-tetrahydrofuran that contains up to 10% by volume of tetrahydrofuran may also be used.
Polymerization according to the invention is possible in batch-type or tube reactors, but is not limited to them; it may be isothermal or adiabatic.
It may be conducted continuously, as described in Patent Application EP-A-0749987 and, in this case, the monomer(s) to be polymerized and the initiation system are first mixed in a micro-mixer (for instance, a micro-mixer of the cyclone or tangential jet type, or the impact-jet type), and the mixture is then injected into the (co)polymerization reactor. The dwell time of the monomer(s) and the initiation system in the micro-mixer is less than the (co)polymerization time.
Homopolymers, random copolymers, block copolymers and polymers or star copolymers are created by the invention.
The monomers that are (co)polymerized by the inventive method are selected particularly from the group composed of (meth)acrylic, vinylaromatic and diene monomers.
The term xe2x80x9c(meth)acrylic monomerxe2x80x9d, as used here, means a monomer selected from among (meth)acrylates of the following respective formulas: 
wherein R0 is selected from among C1-C18 linear or branched alkyl radicals, primary, secondary, or tertiary, C5-C18 cycloakyl radicals, alkoxyalkyl and alkylthioalkyl radicals, wherein the alkyl groups, linear or branched, have 1 to 8 carbon atoms, aryl and arylalkyl, these radicals possibly being substituted by at least one atom of fluorine and/or at least one hydroxyl group after protection of this hydroxyl group; the (meth)acrylates of glycidyl, norbornyl, isobornyl, mono- and di-(alkyl at C1-C18)-(meth)acrylamides.
As examples of usable methacrylates, we cite the methacrylates of methyl, ethyl, 2,2,2-trifluoroethyl, n-propyl, isopropyl, n-butyl, sec.-butyl, tert.-butyl, n-amyl, i-amyl, n-hexyl, 2-ethylhexyl, cyclohexyl, octyl, i-octyl, nonyl, decyl, lauryl, stearyl, phenyl, benzyl, xcex2-hydroxy-ethyl, isobornyl, hydroxypropyl and hydroxybutyl. The preferred methyacrylic monomer is methylmethacrylate.
As examples of acrylates of the above formula, we cite the acrylates of methyl, ethyl, n-propyl, isopropyl, n-butyl, sec.-butyl, tert.-butyl, hexyl, 2-ethylhexyl, isooctyl, 3,3,5-trimethylhexyl, nonyl, isodecyl, lauryl, octadecyl, cyclohexyl, phenyl, methoxymethyl, methoxyethyl, ethoxymethyl and ethoxyethyl.
Vinylaromatic monomer in the sense of this invention means an ethylenically-unsaturated aromatic monomer such as styrene, vinyltoluene, alpha-methylstyrene, methyl-4-styrene, methyl-3-styrene, methoxy-4-styrene, hydromethyl-2-styrene, ethyl-4-styrene, ethoxy-4-styrene, dimethyl-3,4-styrene, tert.-butyl-3-styrene and vinyl-1-naphthalene.
Diene monomer means a diene selected from among the linear or cyclic dienes, conjugated or unconjugated, such as, for example, butadiene, 2,3-dimethyl-butadiene, isoprene, 1,3-pentadiene, 1,4-pentadiene, 1,4-hexadiene, 1,5-hexadiene, 1,9-decadiene, 5-methylene-2-norbornene, 5-vinyl-2-norbornene, 2-alkyl-2,5-norbornadienes, 5-ethylene-2-norbornene, 5-(2-propenyl)-2-norbornene, 5-(5-hexenyl)-2-norbornene.
In particular, the inventive initiation system permits polymerization of PMMA at temperatures of around 0xc2x0 C. and even at temperatures ranging as high as at least 20xc2x0 C., to obtain PMMA with high isotactic triads (which go as high as 75%), with a high mass and a polydispersity index that is low (1.1-1.3).
PMMAs with a high isotactic triad content have the advantage of being able to combine with syndiotactic or radical PMMA or with a block copolymer containing a syndiotactic PMMA block. The stereo complexes formed by these mixtures present the peculiarity of having physical properties different from the two polymers composing them. The thermal properties demonstrated by thermal analyses show the disappearance of the two transition temperatures (Tg) of the homopolymers. The formation of these stereocomplexes causes a physical crosslinking of chains of differing tacticities to form in the mixture. This is of major importance for the mechanical properties of the new materials.
The inventive initiation system also permits:
conducting controlled polymerization of primary acrylates;
conducting the synthesis of (meth)acrylic block copolymers, e.g., poly(alkyl methyl-b-acrylate methylacrylate);
creating an almost quantitative initiation of monomers in pure toluene.
The inventive initiation system is also used for polymerization of diene and vinylaromatic monomers with a narrow polymolecularity. Since these polymers are reactive, other monomers such as methylmethacrylate are introduced after polymerization of a diene or vinylaromatic monomer, to prepare block copolymers that have a narrow polymolecularity index.
In biblock polymers that are obtained pursuant to the invention, for example poly(MMA-b-nBuA), poly(isoprene or butadiene or styrene-b-MMA), the PMMA block advantageously has an isotactic triad content equal to at least 75%.
Note, in particular, that by using the inventive initiation system, it is possible to prepare diene or vinylaromatic-(meth)acrylic block polymers with no need to add, after formation of the first polydiene or polyvinyl-aromatic sequence, a compound such as 1,1-diphenylethylene to decrease the reactivity of carbanions at the end of polydiene or polyvinyl-aromatic chains before initiation of (meth)acrylates (a technique known as xe2x80x9cend-cappingxe2x80x9d).
The following examples illustrate this invention without, however, limiting the scope thereof. In these examples, the following abbreviations were used:
MMA and PMMA=methyl methacrylate and poly(methyl methacrylate);
nBuA=n-butyl acrylate;
sec.-BuLi=sec.-butyllithium;
tert.-BuLi=tert.-butyllithium;
n-BuLi=n-butyllithium;
D3=hexamethylcyclotrisiloxane;